Alprostadil vs Indomethacin: Fundamentally Different Medications
These are completely different medications used for entirely different clinical indications and cannot be directly compared. Alprostadil is a prostaglandin E1 analog used primarily for erectile dysfunction, while indomethacin is a non-steroidal anti-inflammatory drug (NSAID) used for inflammatory conditions like ankylosing spondylitis.
Alprostadil: Erectile Dysfunction Treatment
Mechanism and Indications
- Alprostadil is a synthetic vasodilator identical to prostaglandin E1 that relaxes smooth muscles of the corpus cavernosum and increases cavernous artery diameter to produce erections 1, 2.
- It is FDA-approved as the only single-agent intracavernosal injection therapy for erectile dysfunction in the United States 1, 3.
- Available in multiple formulations: intracavernosal injection (ICI), intraurethral suppository (IU), and topical cream 1, 4, 5.
Clinical Efficacy
- Intracavernosal alprostadil induces erections in approximately 70% of patients with erectile dysfunction of various origins 2.
- Intraurethral alprostadil achieves successful intercourse in 29.5% to 78.1% of patients, with the largest study showing 64.9% success rate 1.
- Superior or equal efficacy compared to other intracavernosal agents like papaverine or papaverine-phentolamine combinations 2, 6.
Administration Requirements
- An in-office test must be performed before prescribing either intraurethral or intracavernosal alprostadil 1, 7.
- The initial dose requires healthcare provider supervision due to risk of syncope (intraurethral) or prolonged erection (intracavernosal) 1, 7.
- Patients need instruction in proper technique and dose titration before home use 1, 7.
Adverse Effects
- Penile pain occurs in approximately one-third of patients but causes only 3-5% to discontinue treatment 2.
- Priapism occurs in 1-4% of patients with intracavernosal use 2, 6.
- Penile fibrosis develops in 2-8% of patients with intracavernosal therapy 2, 6.
- Intraurethral formulation has no reported priapism or fibrosis, making it safer than injection therapy 4.
Indomethacin: Anti-Inflammatory Agent
Mechanism and Indications
- Indomethacin is an NSAID used for inflammatory conditions, particularly ankylosing spondylitis and other spondyloarthropathies 1.
- It works by inhibiting cyclooxygenase enzymes to reduce prostaglandin synthesis and inflammation.
Clinical Use in Ankylosing Spondylitis
- Multiple head-to-head trials used indomethacin as the comparator NSAID, demonstrating no evidence of superior efficacy over other NSAIDs for pain or stiffness 1.
- No particular NSAID, including indomethacin, is recommended as preferred treatment—choice should be based on patient history, risk factors, and comorbidities 1.
Adverse Effects
- Hypertension and depression were more common with continuous NSAID treatment in controlled trials 1.
- Standard NSAID adverse effects include gastrointestinal complications, cardiovascular risks, and renal toxicity.
Key Clinical Distinctions
These medications have no therapeutic overlap:
- Alprostadil treats erectile dysfunction through local vasodilation 1, 2.
- Indomethacin treats systemic inflammatory conditions through prostaglandin inhibition 1.
- They cannot be substituted for one another under any clinical circumstance.
Common Pitfall to Avoid
Do not confuse these medications based on their prostaglandin-related mechanisms—alprostadil is a prostaglandin agonist while indomethacin is a prostaglandin synthesis inhibitor, making them pharmacologically opposite in many respects.